How to reconstitute a peptide
Before you start
Reconstituting means dissolving the freeze-dried powder in a liquid so that it can be measured out and used. It takes a few minutes and needs no special equipment beyond a syringe, a solvent and a clean work surface.
Everything below describes laboratory handling of the materials we supply. It is not advice on use in humans or animals, and we cannot advise on that. Follow your own laboratory's procedures where they differ.
1. Let the vial reach room temperature
Take the vial out of cold storage and leave it sealed until it has reached room temperature. Opening a cold vial lets moisture from the air condense on the powder, and freeze-dried peptide draws in that water readily. If you keep your vials in a desiccator, let them warm up inside it.
2. Decide the volume — that is what sets the concentration
The amount of peptide in the vial is fixed. What you choose is how much liquid to add, and that choice sets the concentration.
Ten milligrams dissolved in 2 mL gives 5 mg/mL. The same ten milligrams in 1 mL gives 10 mg/mL. Nothing else changes. Our reconstitution calculator does the arithmetic for you, including what the concentration corresponds to on a 100 IU syringe.
Choose a volume that leaves the solution easy to measure. Very concentrated solutions make small volumes hard to draw accurately.
3. Choose the solvent
Bacteriostatic water — sterile water with 0.9% benzyl alcohol added as a preservative — is the usual choice when more than one withdrawal will be made from the same vial. The preservative is what allows repeated entries. Sterile water without preservative is used where the preservative would interfere, for example in analytical work; a vial opened that way is a single-use vial.
Not every peptide dissolves in water. Peptide manufacturers give the same order of attempts: test on a small amount first, starting with water. A strongly basic peptide can be taken up in a small volume of dilute acetic acid; a strongly acidic one in a small volume of 0.1% ammonia; a hydrophobic or neutral one in the smallest possible volume of an organic solvent such as DMSO, DMF or acetonitrile.
Whichever you use, dissolve in the small volume first and dilute to the working concentration afterwards. Going straight to a large volume of the wrong solvent leaves the peptide sitting undissolved.
4. Add the liquid slowly, down the wall of the vial
Wipe the rubber stopper with alcohol and let it dry. Draw up the volume you calculated, insert the needle at an angle and let the liquid run down the inside wall of the vial.
Do not aim the stream straight at the cake of powder. A jet hitting the peptide makes it foam, and foaming is mechanical stress on the molecule.
5. Let it dissolve by itself
Swirl the vial gently, or roll it between your fingers. Do not shake it and do not vortex it hard.
Most peptides dissolve in a minute or two. Some take considerably longer — occasionally several hours — and that is normal. If one is slow, a few minutes in a water-bath sonicator helps; keep it from warming up while it is in there.
6. Look at the solution before you use it
A finished solution is clear and free of particles. Cloudiness, fibres or a film on the surface usually mean the peptide has not fully dissolved, or that the solvent is wrong for that sequence. Go back to step 3 rather than shaking harder.
7. Label the vial and store it
Write the substance, the concentration, the solvent and the date on the vial. A solution with no label is a solution you cannot trust a week later.
For short-term use, keep the vial upright at 2–8 °C, protected from light.
For longer storage, divide the solution into single-use aliquots and freeze them below −15 °C; colder is better. Freeze-and-thaw cycles do more damage to a peptide solution than anything else, so thaw only the aliquot you need. Manufacturers do not recommend keeping peptide solutions for long periods — think weeks rather than months — and sequences containing asparagine, glutamine, cysteine, methionine or tryptophan are the least stable of all.
Storing the unopened vials
Sealed, freeze-dried vials keep best cold, dry and dark: below −15 °C for anything beyond short-term storage, and lower still if you have it. The powder is hygroscopic, so close the container again quickly once you have taken a vial out.
What to avoid
Aiming the liquid straight at the powder instead of the vial wall.
Shaking, or vortexing hard, to speed things up.
Warming the vial to make it dissolve faster.
Freezing and thawing the same vial over and over.
Using a solution that has turned cloudy or thrown particles.
Where these instructions come from
The handling and storage steps follow the published technical guidance from peptide manufacturers — Bachem's handling and storage guidelines (bachem.com) and Merck/Sigma-Aldrich's peptide solubility and handling guide (sigmaaldrich.com). The description of bacteriostatic water follows the approved product label for Bacteriostatic Water for Injection, USP (dailymed.nlm.nih.gov).
Our products are supplied for laboratory research use only.